Plugs and sockets are required in the use of electrical appliances using alternating current so as to connect necessary power supply. When there is only one electrical appliance plugged in a socket, the socket may not have a load that is too high. However, when there are multiple electrical appliances plugged in one single socket at the same time, the socket shall very possibly become dangerously overloaded. Safety plug with individual fuse is therefore developed to prevent the possible danger and damage caused by an overloaded socket.
A conventional plug for electrical appliances usually has a simple structure which mainly includes a casing, two pole (positive and negative) pins, and a wire or cable fixedly connected to one end of the casing opposite to the two pole pins.
Please refer to FIG. 7, in which a conventional safety plug 1 is shown. The plug 1 has a casing 12 and an inner sleeve 18. A first pole pin 11 of the plug 1 having a clamping leg 14 is inserted into the sleeve 18 such that the clamping leg 14 engages with a partition plate 13 provided in the sleeve 18 near one side thereof. A cartridge fuse 15 is disposed in the sleeve 18 to contact at a first end with an inward side of the clamping leg 14 so that the cartridge fuse 15 may sense the current flowing from the pole pins to a generally U-shaped fuse terminal 10 disposed at a second end of the cartridge fuse 15 opposite to the first end thereof. When the load of the fuse terminal 10 is too high, fuse wire in the cartridge fuse 15 is burned out and the circuit is open. The casing 12 is formed with a long opening 16 which is opened or closed by means of a top cover 17. The change of new cartridge fuse 15 can be easily done through the long opening 16.
Following disadvantages exist in the above described safety plug:
1. The casing 12 is integrally made of plastic material by means of injection modeling. The inner sleeve 18 is inserted into the casing 12 after the latter is cooled and becomes solid. This assembling manner does not permit convenient and quick replacement and assembling of components inside the casing 12 and therefore requires higher manufacture costs.
2. The cartridge fuse 15 is in a cylindrical form, the first end thereof is connected with the clamping leg 14 of the first pole pin 11 and the second end thereof with the fuse terminal 10. Due to its cylindrical configuration, the cartridge fuse 15 tangentially contacts with the side wall of the clamping leg 14 of the first pole pin 11 and of the U-shaped fuse terminal 10. That is, the cartridge fuse 15 only senses a smaller current tangentially flowing therethrough even though there is actual higher current passing through the circuit. In other words, the cartridge fuse 15 disposed in the plug with the above conventional design can not fully reflect the correctly overloaded current through the burning out of fuse therein. Moreover, whenever the cylindrical cartridge fuse 15 slightly deviates from the side walls of the clamping leg 14 of the first pole pin 11 and/or the U-shaped fuse terminal 10 and separates from the tangential contact with them, it will completely lose its safe-guard function and the electrical appliance on which the cartridge fuse 15 is disposed shall be in an uncertain and dangerous condition.